This Phase II SBIR application proposes the development and testing of a theory-based health promotion mobile phone application, BodiMojo, for adolescents (ages 13-18). The product is designed to: (1) promote wellness, healthy eating and physical activity in adolescents through a mobile program that can be accessed via any cell phone or wireless device; and (2) develop a service administrator tool for health clinics and youth organizations to monitor and reward progress among their youth. Efforts to prevent obesity and improve nutrition intake and physical activity are very challenging to implement with this age group. This is in large part due to difficulties in program uptake and adherence, as well as social stigmatization and a lack of a sense of urgency about potential long-term adverse outcomes in adulthood. Phase I results clearly identified the need to engage teenagers with personal relevancy and to promote positive actions and reward small successes that may lead to behavior change. Attention to psychosocial issues such as mood and body image is clearly key to success in obesity prevention efforts. This project is designed to improve psychosocial factors, including body esteem, mood, and goal adherence, as they mediate the adoption of healthy eating and physical activity behaviors. Based on the proof-of-concept in Phase I, this application intends to fully develop the mobile program using gamification and social networks by capitalizing on the unique and broad-based capability of mobile phones. The second aim will be to develop a web-based tool and manual for health centers and school health staff to engage and track youth members in their efforts toward improving health behaviors. The final aim is to test the efficacy of and adherence to the mobile program in a randomized controlled field study among overweight and obese adolescents who are members of a large HMO. By addressing the unique needs of adolescents in the context of current technological innovations, BodiMojo offers a mobile-based personalized health promotion program that can reach large populations. At the same time BodiMojo facilitates goal attainment, provides empirically-based health information, and offers personalized feedback in a timely and confidential manner that extends beyond the reach of the clinical encounter or educational setting.